This invention relates generally to a design of a thermal ink jet bubble containment chamber and more particularly concerns a containment chamber for absorbing or redirecting acoustic energy.
Generally, an ink jet printing system has a printhead which comprises one or more ink filled channels, communicating with an ink supply chamber at one end and having an opening at the opposite end, referred to as a nozzle. A heating element, usually a resistor, is placed at the bottom of a bubble containment chamber which in turn is located at a predetermined distance from the nozzle. A flow of an electric current heats up the heating element vaporizing the ink in the chamber and forming a bubble. As the bubble grows, the ink is ejected out of the nozzle. By stopping the current flow, the heating element cools off causing the bubble to collapse. While the bubble is collapsing, the ink at the vicinity of the nozzle is pulled in resulting in drop ejection by separation of the ink outside of the nozzle from the ink inside of the nozzle.
It is known in thermal ink jet printing that deposits of dried ink which accumulate at or near the nozzle exit cause the drop ejection accuracy to decrease. The deposits of dried ink are called spattering and are one of the most important factors affecting directionality of the drop ejection. These deposits on the ejection face must be periodically cleaned off as an element of system maintenance. Whether this is done manually or by maintenance station internal to the system, the reduction or elimination of spattering would be highly advantageous. It is observed that the ink on the ejection surface accumulates from very small, aerosol type droplets.
The energy which creates these droplets is acoustic since the collapse of the bubble in the containment chamber is known to proceed to strong cavitation. Indeed, this is the cause of the erosion of the heating element and necessitates the protection of this element with a very strong layer which is, typically, Tantalum. Microphotography indicates that the small problem droplets (spattering) occur when the bubble collapses.
The object of this invention is to eliminate as much as possible the spattering effect. This object is achieved by having the walls of the bubble containment chamber built to have some jagged wedges to absorb or redirect undesired acoustic waves. In a preferred embodiment, four different groups of wedges are built on the walls of the chamber: long wedges located at the rear, opposite to the nozzle exit, dispersive wedges located on the side walls at the front of the chamber close to the nozzle exit, a wide wedge located on the front wall of the chamber and side angle wedges located on the side walls which are adjacent to the dispersive wedges. Each group of wedges serves a different purpose in absorbing or redirecting the undesired acoustic waves.